Metaboo is a variant of the word-describing game "Taboo", where players attempt to communicate a word or phrase to their team-mates without using certain words. Where Taboo requires cards that specifically list the banned words, though, Metaboo only requires a book or a random-word-generator, and allows players to say anything they like.
But it also allows opposing players to interrupt. Instead of avoiding words on a pre-printed list, the describing player has to avoid any words that might help the opposing players. Rather than being an exercise in careful phrasing and thesaurus-speak, Metaboo is about tailoring a description towards a specific person's knowledge (or simply following their apparent train of thought), and trying to avoid other people's.
Metaboo is probably best suited to groups of people who all know one another equally well (or are equally unknown), although it should begin to level out after a few rounds, regardless.
At least three players, and some way of generating random words. A dictionary (or other book) will do - just pick a random page and a random word. If you're playing against people you don't trust, you can get them to choose page and word numbers before looking the word up. (If you're playing on or near the Internet, you can use the Metaboo Word Server.)
If you haven't got any books, ask someone who isn't playing to make words up (or have the Speaker of a round act as word-assigner for the next, and sit that round out).
Pick a random player - he or she is the Speaker.
The Speaker selects another player - that player is the Guesser.
The Speaker receives a random word from wherever the random words come from.
The Speaker then attempts to communicate that word to the Guesser, in such a way that other players are unable to guess it. Any player may guess the word by shouting it out; as soon as anyone has guessed it, the round ends.
If the Speaker successfully communicated the word to the Guesser (ie. the Guesser was the first to guess it correctly), then they each receive a point. If another player guessed the word instead, that player receives a point for intercepting, and the Speaker and Guesser get nothing.
Whoever guessed the word then becomes the Speaker for the next round.
(The winner is the player with most points when people get bored of playing.)
The game can optionally be played as a team game - Speakers only ever select Guessers within their own team, and the other team attempt to "intercept" the word and get control of the game.
Aleric, Boris and Colin are playing. Aleric is the Speaker; he chooses Colin as the Guesser, for this round. Aleric is aware that Colin has read some particular books that Boris hasn't.
Aleric : "The John Wyndham book with the Tennyson quote at the start; the word is a variant of that which covered the world at the end of the book."
Boris : (guessing) "Triffids."
Colin : "Water."
Boris : (seeing where this is going) "Oceans."
Aleric : "Starts with S."
Colin : "Sea. Seaweed."
Boris : "Salt."
Aleric : "No salt."
Colin : "Stream?"
Aleric : "Correct!"